Separation and on‐line preconcentration of nonsteroidal anti‐inflammatory drugs by microemulsion electrokinetic chromatography

The MEEKC separation and on‐line preconcentration of nonsteroidal anti‐inflammatory drugs (NSAIDs) were investigated. In this work, two microemulsion (ME) systems were employed. Complete separation could be achieved at a pH of 5.5 with octane as the oil phase (ME I). The LODs for the determination of flurbiprofen, fenoprofen, naproxen, ketoprofen, suprofen, and indoprofen were 0.45, 0.32, 0.10, 0.48, 0.77, and 0.29 mg/L, respectively. To enhance the sensitivity, anion selective exhaustive injection‐sweeping (ASEI‐sweeping) and stacking with reverse migrating pseudostationary phase (SRMP) were compared. For having a simple process without polarity switching and shorter analysis time, a suppressed EOF and di‐ n ‐butyl‐L‐tartrate as the oil phase (ME II) were used for the simultaneous determination of NSAIDs. The sensitivity for ASEI‐sweeping was enhanced approximately 280‐fold. However, there was much background noise, and some of the analytes were co‐eluted. When SRMP was used, all of the analytes could be detected simultaneously, and baseline separation could be achieved. The sensitivities of all of the analytes, except for indoprofen, were enhanced approximately 170‐fold compared with the normal MEEKC, and the LODs were 2–45 μg/L. Herein, we propose a simple method for the direct determination of NSAIDs at therapeutic and toxic levels in urine throughout a wide concentration range.